U.S. Pat. No. 5,248,856 for CODE-BASED, ELECTROMAGNETIC-FIELD-RESPONSIVE GRAPHIC DATA-ACQUISITION SYSTEM by Mallicoat, issued Sep. 28, 1993, describes a graphic data-acquisition system with respect to which the system of the present invention is an improvement, and is incorporated in this disclosure for illustration purposes. Accordingly, the full disclosure of that patent is hereby incorporated by reference into this disclosure.
That patented data-acquisition system takes the form of a code-based, electromagnetic-field-responsive (and preferably optically responsive) system employing an active pair of transceivers, each including a rotating, multi-faceted scanning mirror and a laser which is thereby scanned across a writing-surface area for the purpose of tracking the position of, and noting certain characteristics respecting, different write-effective components, such as those just mentioned above. While it is very unlikely that someone using, or located near, this kind of a system would ever be in a position to have the beam from a laser in the system directly strike the eye, there is some remote possibility that this could occur. Given this even remote possibility, there is a need for attention, addressed by the present invention, to assure that the system includes certain internal monitoring safety features that will minimize the likelihood of such an occurrence either occurring, or, if occurring, producing any appreciable damage. The system of the present invention, accordingly, and pursuant to a key object of the invention, addresses itself to several concerns relating to imagined situations where laser beam/eye interaction could occur, and focuses on providing internal monitoring and control structures and substructures which reduce, as much as possible, the likelihood of a catastrophic eye/laser-beam encounter.
In particular, when a graphic, data-acquisition system of this type is in normal operation, a laser beam typically is scanned in successive scanning sweeps through a scanning zone which is located near a writing-surface area, and there is some possibility that an object impinged in that zone by the laser beam could reflect outwardly toward the eye of a nearby person. To deal with this possibility, the system of the present invention, inter alia, forces on such a beam what might be thought of as a controlled operating duty cycle, whereby the "effective" power of the beam, during normal operation, is reduced well below the nominal operating power level for the beam. Specifically, the system of the invention utilizes a blanking/un-blanking control "mechanism" and signal, whereby the particular laser involved operates for only a short period of time relative to each revolution of a multi-faceted scanner.
Backing this up, and as a further safety measure, the system of the invention incorporates substructure which monitors the blanked or "sleeping" period of time for the laser to assure that if, for some reason, the laser does not shut down to what is referred to herein as a "sleeping" power level, power flow is completely and immediately shut off to the laser and to the scanner.
A further safety consideration taken into account in accordance with the invention is that the laser is not permitted to be powered except under circumstances when (1) the drive motor for the associated scanner is enabled and (2) the associated driven scanner is in fact operating at full scanning speed, or rpm.
Finally, the safety features of the invention include controls whereby when a user of the system gives a command to shut down system operation, power is immediately cut off from the laser.
Thus, in addition to providing positive control over the effective operating power of a scanned laser during normal operation, the system of the present invention monitors other areas of "normal" activity, and disables the laser when a related abnormality appears.